Plants have been one of the important sources of medicines ever since the dawn of human civilization. Human beings have been utilizing plants for basic preventive and curative health care since time immemorial. Recent estimates suggest that over 9000 plants have known medicinal applications in various cultures and countries. According to the WHO World Health Organization over 80 % of the world's population, or about 4.3 billion people, rely upon such traditional plant based systems of medicine to provide them with primary health care.
Demand for medicinal plants is increasing in both developing and developed countries due to growing recognition of natural products, being non-narcotic, having no side-effects, easily available at affordable prices, and sometimes are the only source of health care available to the poor. The medicinal plant sector has traditionally occupied an important position in the socio-cultural, spiritual and medicinal arena of rural and tribal lives of India. The medicinal plants sector in India supports primary health care needs of most of the country's population even today.
Chemically, depending on their active principles, plants may have alkaloids, glycosides, steroids or other groups of compounds, which may have marked pharmaceutical actions as anti-cancerous, anti-malarial, anti-helminthic or anti-dysenteric, etc. Among the most important materials with which pharmacologists manufacture drugs are alkaloids complex bio-compounds produced by many categories of plants. Plant alkaloids including cocaine, reserpine, quinine, ipecac, ephedrine, caffeine, nicotine etc. have many medicinal applications.
About 80% of all known green plants are flowering plants or angiosperms, most of which are found in the tropical rainforests of the world. Rainforest plants are rich in secondary metabolites, particularly alkaloids. Biochemists believe that alkaloid protect plants from disease value and benefit. Medicinal plants have thus gained pharmaceutical importance or therapeutic value due to the specific constituents or combination of secondary metabolites present in them. In some cases, changes in the relative proportion and quantity of secondary metabolites are often required for the improvement of therapeutic values of medicinal plants. Most of biomolecules of the medicinal plants with therapeutic value are the secondary metabolites. These molecules are produced in very small quantities and in specific tissue of the plant. This makes their extraction process cumbersome and expensive.
Most researchers working in this area have so far and are still focussing on identifying tropical rainforest plants as a source of compounds useful for medicinal purposes, but have never attempted to identify common weed as its source. Till date tropical rain forest is considered important for medicinal plants, however common weeds have been neglected, which too have medicinal value. Medicinal Plants are far more likely to be weeds growing alongside a dirty road than in an exotic tropical jungle.
Weeds are the plants that thrive in the wild and can establish themselves quickly in relatively harsh agroclimatic conditions. The term “weed” in broadest sense implies to any plant growing where it is not wanted. Weeds can be native or non-native, invasive or non-invasive, and noxious or non-noxious. The weed used in the present invention is a non-invasive type. It is a known fact that weeds because of their genetic make up grow in the extreme climate. They relatively have higher concentration of secondary metabolites, which make them ideal source for genetic manipulation by modulation of the respective genes. While, considerable scientific attention has been given to the potential value of cultivated and tropical medicinal plants, very little research has been done on the potential of common weeds. Solanum viarum is one such neglected weed plants.
Solanum viarum belongs to the family of Solanaceae. Solanum viarum Dunal commonly known as “tropical soda apple” holds an important place as a source for production of medicinal drugs, due to relatively high level of steroidal alkaloids present in it. Solanum viarum can be cultivated on a wide range of soils under various agroclimatic conditions, but it cannot withstand waterlogging also the plant does not perform well in very clayey soils.
Solanum viarum yields a glycol-alkaloid, solasodine, a nitrogen analogue of diosgenine. Solasodine through 16-dehydro pregnenolone (16 DPA) is converted to a group of compounds like testosterone and methyl testosterone and corticosteroids like predinisolone and hydrocortisone. These steroidal compounds have anti-inflammatory anabolic and antifertility properties, due to which they are largely used in health and family planning programs all over the world. Solasodine presents several glucocorticoid like effects. It is effective against hypocholestrolamemic and antiatherosclerotic diseases. It enhances the glucocorticoid secretion by adrenal glands. In prolonged use, it causes atrophy of the adrenal gland cortex. Solasodine glycosides have an ability to check cytotoxicity of cancer cells.
In Solanum viarum, solasodine alkaloid is distributed throughout the fruits. It is however, established that about 60% of this is present the seeds and the remaining 40% in the pericarp. Generally, the accumulation of glycol alkaloid increases with the physiological age of the fruit and attains its peak value in the fruits of 50-60 days. This state of fruit growth coincides with the change in fruit colour from green to just yellow with streaks of green still present, after which the glycol alkaloid content falls gradually with the maturity of fruits. The crop takes about 6 months to be ready for harvesting. When, the crop is grown by adopting proper cultivation practices, it may yield nearly 10,000 kg/ha of fresh berries which, in turn, will give about 2500 kg/ha of dried berries. However considering the use of mature fruits as a source for production of medicinally important steroidal alkaloids, the availability of the seeds as a planting material is the most limiting factor for its cultivation.
Moreover, some Solanum viarum is a weed, and the seeds are the mode of multiplication which could result from a cross-pollination and may also result in genetic drift. This may affect the content of medicinally very important chemical constituents like solasodine. Therefore, there exists a need for an efficient system of vegetative multiplication which ensures its genetic uniformity and true to the type of nature.
Biotechnological tools are important to multiply, select, and conserve the critical genotypes of medicinal plants by adopting techniques such as micropropagation, creation of somaclonal variations and genetic transformation. Biotechnological tools can also be harnessed for production of secondary metabolites using plants as bioreactors. In-vitro propagation involves tissue culture system by multiplication of meristems and auxiliary buds. In many cases it provides opportunity to maintain true to type plant species and the propagation system can produce a large number of plants from a single clone.
Tissue culture is basically defined as in vitro growth of plantlets from any part of the plants in a suitable nutritive culture medium. It is also known as ‘micropropagation’in scientific technology. Tissue culture is a means of preserving species that are rare and threatened and providing an alternative source of plants for commercial horticultural and traditional medicinal trade. Tissue culture involves the aseptic culture of plant protoplasts, cells, tissues, or organs on a culture medium. The cultures are maintained under controlled environmental condition. The main difficulty in conventionally growing indigenous plants in large quantities is to obtain sufficient plant material. Seeds may germinate erratically and bulbs usually propagate by offsets. This makes production too slow to warrant their introduction as new commercial crops. In vitro methods are therefore used to speed up propagation. The success of the system lies in the development of strict protocols for each species.
Micropropagation has been defined as in vitro regeneration of plants from organs, tissues, cells or protoplast and results in the true to type propagation of a selected genotype using in vitro culture techniques. In essence, tissue from a plant (explant) is isolated to create a sterile tissue culture of that species in vitro. Once a culture is stabilized and growing well in vitro, multiplication of the tissue or regeneration of entire plant can be carried out. Commonly shoots (tips, nodes or internodes) and leaf pieces are used however cultures can also be generated from many different tissues as well. Juvenile tissues generally respond best. With genotypes, the physiological age and origin of explants as well as the chemical composition of the culture medium and the physical environment of cultures have been found to influence growth and development of new plants in the culture system, hence one need to optimize these for each of the genotype.
In summary micropropagation of a given genotype, using tissue culture is targeted to achieve the following:                Rapid, large scale, year round production of desired plant species.        Propagation of plant species where, there is difficulty to grow the plants on large scale from seeds, because of the scarcity of seeds due to its use for other purposes.        Production of genetically uniform plant material (clones).        Production of disease free plant material.        
Up to the present date, large-scale micropropagation using tissue culture of Solanum viarum has not been attempted, as Solanum viarum is a wild type of weed. Hence, not much attention has been paid to the improvement of the plant species in spite of important metabolites it produces. Also, there is no organized cultivation of this plant species for commercial utilization. It is simply collected from the wasteland or jungle. Therefore, there exists a need to develop an efficient in-vitro system for large-scale micropropagation of Solanum viarum. 